The invention relates to a magnetic-path member through which magnetic lines of force produced by an electromagnet pass, an electromagnetic coupling device using the magnetic-path member, and a method of manufacturing the magnetic-path member.
Japanese Unexamined Patent Publication Laid-open No. Hei 11-153157 discloses a driving-force transmission device. In this driving-force transmission device, an electromagnet attracts an armature to engage a pilot clutch (friction clutch). The pilot clutch actuates a cam mechanism by the driving force of an engine that acts on the cam mechanism through the pilot clutch. The cam mechanism engages a main clutch mechanism under the thrust power thereof.
The magnetic lines of force from the electromagnet are applied from a magnetic rotor (rear housing) through the pilot clutch to the armature. The rotor is magnetically partitioned by a non-magnetic ring (annular portion), thus preventing short circuits between outgoing and returning magnetic lines of force. This ring is welded to the rotor by electron beam welding.
In electron beam welding performed in this driving-force transmission device, welding is performed along the entire perimeter of the ring, and therefore operating time becomes longer accordingly. This deteriorates the productivity thereof. Electron beam welding is tends to produce uneven welding. Variations in cutting which are caused by the uneven welding causes the shaping of the ring and the rotor to be difficult, thus varying the quality.
The invention provides an excellent-productivity, low-cost, and stable-quality magnetic-path member, an electromagnetic coupling device using this magnetic-path member, and a method of manufacturing the magnetic-path member.